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using popen shows WindowsError: [Error 2] The system cannot find the file specified

windows 7 python 2.7
when I use popen to open a process：
from ctypes import *
dldtool = cdll.LoadLibrary(r'main.dll')
cmd = "dld_tool -c {} -r programmer.bin -f {}".format(port,file)
print cmd
with LOCK:
process = Popen(cmd, stdout=PIPE)
while process.poll() is None:
out = process.stdout.readline()
if out != '':
print out
error occurs：
process = Popen(cmd, stdout=PIPE)
File "C:\Python27\lib\subprocess.py", line 390, in __init__
errread, errwrite)
File "C:\Python27\lib\subprocess.py", line 640, in _execute_child
startupinfo)
WindowsError: [Error 2] The system cannot find the file specified
The main.dll is in the working directory. should I change the code in python or change the any config?

You should use either the shell=True parameter if you want to pass the entire command with arguments as one string:
process = Popen(cmd, stdout=PIPE, shell=True)
or shlex.split to split your command line into a list (after importing shlex):
process = Popen(shlex.split(cmd), stdout=PIPE)
Otherwise the entire command line with arguments would be treated as one file name, and the system naturally would not be able to find it.

subprocess.Popen() error (No such file or directory) when calling command with arguments as a string

I am trying to count the number of lines in a file using Python functions. Within the current directory, while os.system("ls") finds the file, the command subprocess.Popen(["wc -l filename"], stdout=subprocess.PIPE) does not work.
Here is my code:
>>> import os
>>> import subprocess
>>> os.system("ls")
sorted_list.dat
0
>>> p = subprocess.Popen(["wc -l sorted_list.dat"], stdout=subprocess.PIPE)File "<stdin>", line 1, in <module>
File "/Users/a200/anaconda/lib/python2.7/subprocess.py", line 710, in __init__
errread, errwrite)
File "/Users/a200/anaconda/lib/python2.7/subprocess.py", line 1335, in _execute_child
raise child_exception
OSError: [Errno 2] No such file or directory

You should pass the arguments as a list (recommended):
subprocess.Popen(["wc", "-l", "sorted_list.dat"], stdout=subprocess.PIPE)
Otherwise, you need to pass shell=True if you want to use the whole "wc -l sorted_list.dat" string as a command (not recommended, can be a security hazard).
subprocess.Popen("wc -l sorted_list.dat", shell=True, stdout=subprocess.PIPE)
Read more about shell=True security issues here.

The error occurs because you are trying to run a command named wc -l sorted_list.dat, that is, it is trying to find a file named like "/usr/bin/wc -l sorted dat".
Split your arguments:
["wc", "-l", "sorted_list.dat"]

Subprocess in Python: File Name too long

I try to call a shellscript via the subprocess module in Python 2.6.
import subprocess
shellFile = open("linksNetCdf.txt", "r")
for row in shellFile:
subprocess.call([str(row)])
My filenames have a length ranging between 400 and 430 characters.
When calling the script I get the error:
File "/usr/lib64/python2.6/subprocess.py", line 444, in call
return Popen(*popenargs, **kwargs).wait()
File "/usr/lib64/python2.6/subprocess.py", line 595, in __init__
errread, errwrite)
File "/usr/lib64/python2.6/subprocess.py", line 1106, in _execute_child
raise child_exception
OSError: [Errno 36] File name too long
An example of the lines within linksNetCdf.txt is
./ShellScript 'Title' 'Sometehing else' 'InfoInfo' 'MoreInformation' inputfiile outputfile.txt 3 2
Any ideas how to still run the script?

subprocess.call can take the command to run in two ways - either a single string like you'd type into a shell, or a list of the executable name followed by the arguments.
You want the first, but were using the second
import subprocess
shellFile = open("linksNetCdf.txt", "r")
for row in shellFile:
subprocess.call(row, shell=True)
By converting your row into a list containing a single string, you're saying something like "Run the command named echo these were supposed to be arguments with no arguments"

You need to tell subprocess to execute the line as full command including arguments, not just one program.
This is done by passing shell=True to call
import subprocess
cmd = "ls " + "/tmp/ " * 30
subprocess.call(cmd, shell=True)

data stream python subprocess.check_output exe from another location

I would like to run an exe from this directory:/home/pi/pi_sensors-master/bin/Release/
This exe is then run by tying mono i2c.exe and it runs fine.
I would like to get this output in python which is in a completely different directory.
I know that I should use subprocess.check_output to take the output as a string.
I tried to implement this in python:
import subprocess
import os
cmd = "/home/pi/pi_sensors-master/bin/Release/"
os.chdir(cmd)
process=subprocess.check_output(['mono i2c.exe'])
print process
However, I received this error:
The output would usually be a data stream with a new number each time, is it possible to capture this output and store it as a constantly changing variable?
Any help would be greatly appreciated.

Your command syntax is incorrect, which is actually generating the exception. You want to call mono i2c.exe, so your command list should look like:
subprocess.check_output(['mono', 'i2c.exe']) # Notice the comma separation.
Try the following:
import subprocess
import os
executable = "/home/pi/pi_sensors-master/bin/Release/i2c.exe"
print subprocess.check_output(['mono', executable])
The sudo is not a problem as long as you give the full path to the file and you are sure that running the mono command as sudo works.
I can generate the same error by doing a ls -l:
>>> subprocess.check_output(['ls -l'])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.7/subprocess.py", line 537, in check_output
process = Popen(stdout=PIPE, *popenargs, **kwargs)
File "/usr/lib/python2.7/subprocess.py", line 679, in __init__
errread, errwrite)
File "/usr/lib/python2.7/subprocess.py", line 1249, in _execute_child
raise child_exception
OSError: [Errno 2] No such file or directory
However when you separate the command from the options:
>>> subprocess.check_output(['ls', '-l'])
# outputs my entire folder contents which are quite large.
I strongly advice you to use the subprocess.Popen -object to deal with external processes. Use Popen.communicate() to get the data from both stdout and stderr. This way you should not run into blocking problems.
import os
import subprocess
executable = "/home/pi/pi_sensors-master/bin/Release/i2c.exe"
proc = subprocess.Popen(['mono', executable])
try:
outs, errs = proc.communicate(timeout=15) # Times out after 15 seconds.
except TimeoutExpired:
proc.kill()
outs, errs = proc.communicate()
Or you can call the communicate in a loop if you want a 'data-stream' of sort, an answer from this question:
from subprocess import Popen, PIPE
executable = "/home/pi/pi_sensors-master/bin/Release/i2c.exe"
p = Popen(["mono", executable], stdout=PIPE, bufsize=1)
for line in iter(p.stdout.readline, b''):
print line,
p.communicate() # close p.stdout, wait for the subprocess to exit

subprocess piping output on Windows

I've got this piece of code that works fine on Linux but fails on Windows. Process is created fine, but I get an error and nothing is read from pipe:
p = subprocess.Popen(['python', '-u', self.file_to_run,
'-s', '-g', '-i', self.input_file],
universal_newlines=True,
stdout=subprocess.PIPE)
...
out = p.stdout.readline().rstrip()
Error I get is
Traceback (most recent call last):
File "bench.py", line 59, in <module>
multi.add_process()
File "bench.py", line 47, in add_process
stdout=subprocess.PIPE)
File "c:\python\v2.5.1-ast3\...\lib\subprocess.py", line 615, in __init__
self.stdout = os.fdopen(c2pread, 'rU', bufsize)
OSError: [Errno 22] Invalid argument
I actually create multiple such processes and based on their output calculate some values, but that is irrelevant. What I need to do is, run the script with certain arguments multiple times and parse the data piped from stdout of each process.

try using sys.executable instead of 'python' in your subprocess args. I think this is because Python is not in the PATH on Windows.
Also check the value of self.file_to_run and self.input_file which must be strings and not None or strange stuff, but this probably won't cause an OSError.